Millions of binder-ligand assays are performed throughout the world annually, effecting virtually every discipline within medicine. Still, many basic principles of assay design remain poorly understood. This project is an attempt at comprehensive mathematical modeling (computer simulation) of one type of binder-ligand assay, radioimmunoassay. The computer model combines a chemical kinetic model for the constituents of the assay reactions with a statistical model for the various sources of random error in the assay method. One particular strength of the model is its ability to simulate disequilibrium assays. Important assay performance parameters such as imprecision, response, error in response, and slope of calibration curve, can be examined as functions of any two assay parameters, utilizing contour mapping procedures, thus allowing the study of assay ruggedness. Two-dimensional plots such as calibration curves, Scatchard plots, Hill-Sips plots, imprecision profiles and response-error relationships can also be produced.